Since Princeton’s Dr. Michael Oppenheimer conflated weather with climate last week, proclaiming a short lived heat wave as “This is what global warming really looks like” in a media interview, it seems only fair to show what real science rather than what he and Dr. Trenberth’s government funded advocacy looks like. I can’t wait to see how Dr. Michael Mann tries to poo-poo this one. – Anthony
From Johannes Gutenberg-Universität Mainz: Climate in northern Europe reconstructed for the past 2,000 years: Cooling trend calculated precisely for the first time
Calculations prepared by Mainz scientists will also influence the way current climate change is perceived / Publication of results in Nature Climate Change
An international team including scientists from Johannes Gutenberg University Mainz (JGU) has published a reconstruction of the climate in northern Europe over the last 2,000 years based on the information provided by tree-rings. Professor Dr. Jan Esper’s group at the Institute of Geography at JGU used tree-ring density measurements from sub-fossil pine trees originating from Finnish Lapland to produce a reconstruction reaching back to 138 BC. In so doing, the researchers have been able for the first time to precisely demonstrate that the long-term trend over the past two millennia has been towards climatic cooling.
“We found that previous estimates of historical temperatures during the Roman era and the Middle Ages were too low,” says Esper. “Such findings are also significant with regard to climate policy, as they will influence the way today’s climate changes are seen in context of historical warm periods.”
The new study has been published in the journal Nature Climate Change.Was the climate during Roman and Medieval times warmer than today? And why are these earlier warm periods important when assessing the global climate changes we are experiencing today? The discipline of paleoclimatology attempts to answer such questions. Scientists analyze indirect evidence of climate variability, such as ice cores and ocean sediments, and so reconstruct the climate of the past. The annual growth rings in trees are the most important witnesses over the past 1,000 to 2,000 years as they indicate how warm and cool past climate conditions were.
Researchers from Germany, Finland, Scotland, and Switzerland examined tree-ring density profiles in trees from Finnish Lapland. In this cold environment, trees often collapse into one of the numerous lakes, where they remain well preserved for thousands of years.The international research team used these density measurements from sub-fossil pine trees in northern Scandinavia to create a sequence reaching back to 138 BC. The density measurements correlate closely with the summer temperatures in this area on the edge of the Nordic taiga.
The researchers were thus able to create a temperature reconstruction of unprecedented quality. The reconstruction provides a high-resolution representation of temperature patterns in the Roman and Medieval Warm periods, but also shows the cold phases that occurred during the Migration Period and the later Little Ice Age.In addition to the cold and warm phases, the new climate curve also exhibits a phenomenon that was not expected in this form.
For the first time, researchers have now been able to use the data derived from tree-rings to precisely calculate a much longer-term cooling trend that has been playing out over the past 2,000 years.
Their findings demonstrate that this trend involves a cooling of -0.3°C per millennium due to gradual changes to the position of the sun and an increase in the distance between the Earth and the sun.”This figure we calculated may not seem particularly significant,” says Esper. “However, it is also not negligible when compared to global warming, which up to now has been less than 1°C. Our results suggest that the large-scale climate reconstruction shown by the Intergovernmental Panel on Climate Change (IPCC) likely underestimate this long-term cooling trend over the past few millennia.”
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Orbital forcing of tree-ring data
Jan Esper, David C. Frank, Mauri Timonen, Eduardo Zorita, Rob J. S. Wilson, Jürg Luterbacher, Steffen Holzkämper, Nils Fischer, Sebastian Wagner, Daniel Nievergelt, Anne Verstege & Ulf Büntgen
- Received 27 March 2012 Accepted 15 May 2012 Published online 08 July 2012
Solar insolation changes, resulting from long-term oscillations of orbital configurations1, are an important driver of Holocene climate2, 3. The forcing is substantial over the past 2,000 years, up to four times as large as the 1.6 W m−2 net anthropogenic forcing since 1750 (ref. 4), but the trend varies considerably over time, space and with season5. Using numerous high-latitude proxy records, slow orbital changes have recently been shown6 to gradually force boreal summer temperature cooling over the common era. Here, we present new evidence based on maximum latewood density data from northern Scandinavia, indicating that this cooling trend was stronger (−0.31 °C per 1,000 years, ±0.03 °C) than previously reported, and demonstrate that this signature is missing in published tree-ring proxy records. The long-term trend now revealed in maximum latewood density data is in line with coupled general circulation models7, 8 indicating albedo-driven feedback mechanisms and substantial summer cooling over the past two millennia in northern boreal and Arctic latitudes. These findings, together with the missing orbital signature in published dendrochronological records, suggest that large-scale near-surface air-temperature reconstructions9, 10, 11, 12, 13 relying on tree-ring data may underestimate pre-instrumental temperatures including warmth during Medieval and Roman times.
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I’m sure Steve McIntyre will give this paper a thorough examination for the same sorts of issues we’ve seen before in MBH98. Hopefully he won’t have to beg for years to get the data for replication like he did with Mann.
h/t to WUWT readers “Typhoon” and Dr. Leif Svalgaard
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timg56 says:
July 9, 2012 at 3:31 pm
Just curious, but if people have doubts about the quality of tree rings as temperature gauges, is there any reason to accept this with open arms?
#####
1. Maximum latewood density
2. Esper
3. rob wilson
4. Zorita
That’s 4 reasons. 1 technical and 3 based on the quality of prior work,
Why should I suddenly start to believe any study involving tree rings as a proxy for temperature?
I maintain that tree rings are an unreliable thermometer and any reconstruction based on tree rings cannot accurately show temperature. If you combine this reconstruction with Briffa’s and Mann’s and all the others, you get a mess of contradictory information whose only worth is to tell you that tree ring based reconstructions are complete bunkum.
Which is also a useful way to show, categorically, that Mann’s Hockey stick is utter rubbish.
Really not sure about the use of tree rings to tell us anything other than growth rate & age of a tree. Dendrochronology has it’s place for dating trees, but for me dendrochronology when used as a thrermometer is akin to phrenology to determine a psycholigical profile
At least, this study makes sense.
Bearing in mind how sceptical we are of Manns tree rings- or indeed any tree rings- we should not get excited because this one shows a story we like. Tree rings ae terrible proxies for temperatures for reasons previously cited, including their recordng a signal only during a short active growin season.
The lack of an LIA during the 17th Century when we have extremely good records for this period and other periodic cold bursts later, suggests that the study should be taken with a pinch of salt. Incidentally pre Mann we had always known of the greater warmth of the Minoan and Roman and MWP compared to today
tonyb
sorry. Just noticed the caption that this chart shows summer temperatures. which reduces the studies usefulness somewhat. It wasthe winters that dragged the overall mean temperature down-many LIA summers were very hot
tonyb
tornadomark says: July 9, 2012 at 3:23 pm How many want to bet that the Warmists will now declare tree rings unreliable?
I’ve already declared that for me, tree rings are unreliable for thermometry reconstruction. Nothing in this paper changes my attitude. My attitude is not driven by “like” or “dislike” of the outcome. Look past the pretty picture and remember the many pages of discussions of unsolved and unsolvable problems with the method.
It’s not particularly important to estimate temperatures over the last 2,000 years. It’s more important to decide NOW if there is a real and present threat to an important part of the globe or its products and to remediate if wise.
As for me and where I live, nature’s impact on my life is much like 60 years ago. Can’t see why people are getting so fussed. My main problem is a decline in the quality of Science. I nearly died from laughter at Climategate, catching the kids with their hands in the cookie jars. One cartoon vignette followed another.
Here’s to Climategate Tranche #3.
SteveSadlov “In a relatively moisture rich environment in the mid latitudes treemometers sort of work. Elsewhere, not so much.”
Trees respond to the dominant controlling factor. If that is not water, then it allows more influence of temperature, but we are still left with the problem of “canopy adaptation”. The problem is that trees will grow until no more trees can grow. It does not matter whether it is the middle of the tropical jungle, or the sparse canopy of the north, the fact is that if more trees could grow, they would. So, if conditions “improve” the result may be a spurt in growth for individual trees, but it is also likely that more trees can grow, and fairly rapidly (a few decades), there will be more trees, these trees then compete reducing growth for other trees so that any individual tree will tend towards its optimum growing conditions.
A better analogy would be rats … if you put out a tonne of rubbish … there will be a tonne’s worth of rats. Put out two tonnes or rubbish, suddenly all the rats are a lot bigger — hey presto, it appears that rat size is a proxy for food output (just like trees and growing conditions) but then, they all grow quickly until, there is a population of rats that can be sustained by 2tonnes of rubbish and (unless something else limits them) each individual rat will grow as quickly with 2 tonnes of rubbish as with one. … and in the long term the size of rats tells you nothing about the availability of foot … only the number of rats is a proxy for food, not the size.
Likewise, with trees. Over the lifetime of any tree, the whole canopy will adapt so that the number of trees tend toward the same growing conditions for any one tree. The total bulk of wood is a proxy for growing conditions, the growth of any tree is dependent on canopy density and growing conditions. Of course, it’s more complicated than this, but fundamentally, the long term response is that of a population of trees which is very different from the short term response of any single tree.
But, the big problem with all tree-ring studies, is that they calibrate temperature response against the response of individual trees (before the canopy can adapt), whereas the key signal we want to know about is long term change which is dominated by the response such as changes in tree density of the canopy as a whole
To give another analogy, tree rings are a bit like measuring sea level changes (aka waves) by watching the water on the side of a ship. This method is very good at spotting rough seas where the change is smaller than the length of the ship … because the ship’s position doesn’t change much. But as soon as you start getting waves longer than the ship, the whole ship starts moving up and down. And when you look at changes in tide-level, there is absolutely no response (unless the ship grounds) … in which case, you tend to get a non-linear (lopsided) response.
“How many want to bet that the Warmists will now declare tree rings unreliable?”
And the skeptics will now accept the tree ring reconstructions…. :-))))))))))
The paper cuts both ways. The cooling trend makes MWP less dramatic compared to the trend rather than the long term average. (Of course the Hockey Stick had long term gentle cooling already.) I suspect this result will be welcomed into the fold.
Addendum (to last comment on canopy adaptation)
Paradoxically, the best proxies to use are:
1. Those with a lifetime much less than the available temperature record. Which means typically less than 10 years, as it is possible to calibrate for canopy adaptation using available temperature data (ideally annuals are best … as the canopy grows each year). Alternatively, the lifetime should be much much greater than the period of reconstruction, so that over the period of reconstruction there is almost no canopy change. So that means e.g. that a 1000year old tree, is probably only reliable as a proxy for around 100years – which makes all trees practically useless – we would need trees around since the ice-age to get anything decent for the last 1000 years.
So, As a rule of thumb, trees are only a reliable proxy for changes occurring within 10% (an engineer, not biologist’s guess for the rate of canopy adaptation) of their lifetime. So, e.g. a tree that lives for 400 years, may be able to tell us a great deal about a decade of cooler temperature due to some volcano (which is why some academic are so deluded about their ability), but it is completely useless at telling us whether the climate was generally cooler or warmer 400 years ago.
Gaudenz Mischol says:
And the skeptics will now accept the tree ring reconstructions…. :-))))
NO !!! , only as another possible piece of the puzzle
Mann’s use of trees was basically fraud on the statistical side of things, these guys look like they may have a bit better understanding. We will see if they produce the data and how they came to their conclusions so others can check it.. That is a VERY GOOD pointer to scientific honesty, sadly missing in most climate science.
SS;
Nice point; measure the forest, not the trees. It’s even more directly relevant; after all, we’re trying to project the fate of the human forest.
of course…. penny just dropped. Zorita, Luterbacher, Esper, Timonen…
This is the way the Team are distancing themselves from Mikey Mann.
Now Mann’s cover is blown, with everyone knowing exactly why, the others still need to keep the grants flowing. Cynical, but realistic. But also, with no acknowledgement to Steve McIntyre evident here, it means that this portion of Climate Science looks set on the road to recovery….
If the data and metadata are archived and auditable…
According to this their instrumental data and the tree ring data shows no significant warming since WWII. So the weather in Finland isn’t getting any better then!
I suspect that tree ring data will go the way of ice-core data and gradually cease to be mentioned. Team-AGW will be left with snail shells and thermometers placed at airports soon.
I suspect their slight bow to ‘anthropogenic forcing’ is the main reason this got published in this journal… without it, would we have seen it?
fredberple:
“In other words, it isn’t the trees that are at fault. It is the knuckleheads looking at the tree cores that have improperly applied amplifier technology to statistics, thinking they were inventing a better way to look at noisy data. What they invented instead was a way to amplify noise, while making it look like signal. They fooled not only themselves, but most of the world as well.”
For me this is an eye-opener. Suppose you have a complex sound as produced by thousands of sound sources. Next, you silence those sources having the lowest correlations with the envelope. Repeat this procedure again and again and you will have in the end an artificial signal. This is precisely what happened during the great dying of the thermometers late twentieth century. No wonder that the surface and satellite records diverged.
@davidmhoffer
A single tree doesn’t tell us anything. IIRC Finnish Forestry Institute uses minimum of 50 trees to determine the temperature for each year.
And the treeline on mountains is a good calibrator. If the trees cannot grow nowhere near where they grew 800 years ago because it is too cold, then we can reasonably conclude that it was warmer previously.
But there are other ways to determine the temperature. I know people from the Finnish Geology Department and they say that meltwater runoff is not detectable during the MWP anywhere on Finland south of Jyväskylä. This translates to snowless winters in areas we now have typically around 100cm of sno every winter. The tree rings confirm this.
Reading this caused me to go back and reread a paper from 2005 by Ulrich Joerin et al at the University of Bern http://www.climate.unibe.ch/~stocker/papers/joerin06hol.pdf. They study tree trunks and peat deposits that are released from melting glaciers in the Swiss alps. Of course a tree can only get in to a glacier in the first place if at some time in the past the tree line was significantly higher than today, as the tree line today is at the altitude of the glacial tongue (ie approx 2,000m in the Alps). Thus their method is very good at giving information on glacial recessions, ie periods when glaciers and temperatures were higher than today in the Alps. They indeed provide further evidence that glaciers were much higher in the Alps than today during the MWP and RWP and others. But the really interesting conclusion , which links to today’s post, is in the conclusion of the Joerin paper: “….it is suggested that major glacier fluctuations
occurred on a multicentennial scale and that their pattern changed from long recessions (/500 yr) interrupted by short advances (B/200 yr) during the early Holocene to the opposite pattern with relatively short recessions and prolonged advances during the late Holocene (after 3.3 cal. kyr BP). It is important to recognize that this natural variability of glacier extent, which occurs on a centennial timescale, is superimposed on a much longer term, multimillennial-scale trend towards increased glacier extent culminating in the ‘Little Ice Age’.
In other words, they conclude that throughout the Holocene, the warm periods have been getting shorter and the cool periods longer. If that is indeed the case thank god for AGW for saving is from an accelerated decline into re-glaciation!
Where are the error bars on the reconstruction?
What is the instrumental record they use where the 40’s are warmer than now?
Old Arrhenius was right. We have to fear the ice age and pump CO2 like the world’s about to end.
Conclusions should not be taken too far. They calibrated against JJA temperatures of 3 stations in the common period:
“The MXD climate signal was assessed using Pearson correlation coefficients between the lakeshore subsets Ket-L (r = 0.74), Kir-L (r = 0.75) and Tor-L (r = 0.74) and mean JJA temperatures recorded at the global historical climatology network stations Haparanda, Karasjok and Sodankyla over the 1876–2006 common period. Running correlations were applied to analyse the temporal characteristics of the signal revealing reduced coherence among the station records as well as between the station and proxy data centred in the 1910s (Supplementary Fig. S10). The long-term N-scan record integrating lakeshore and subfossil MXD data correlates at 0.77 (r2 = 0.59) with regional JJA temperatures. We transferred this record into a JJA temperature reconstruction using ordinary least square regression with MXD as the independent variable. This approach provides conservative estimates—owing to the reduction of variability caused by unexplained variance29—of pre-instrumental climate variability and derived long-term trends.”
They mention variance loss here!
Good comment by Henry Clark.
Tim Ball says: July 9, 2012 at 4:21 pm
All the actual records show that it is winter temperatures that change the most.
Exactly what CET the world longest and most accurate temperature record shows as plotted here:
http://www.vukcevic.talktalk.net/CETsw.htm